Patent Literature 1, for example, discloses an actuator that uses a ball screw mechanism to convert a rotation of an electric motor into a linear motion by which a driven mechanism is caused to operate. Patent Literature 2 discloses a bidirectional actuator performing a rotational operation and a linear operation simultaneously so that a protruding end of the rotation shaft is caused to move rotationally and linearly smoothly along a given path.
Patent Literature 3, for example, discloses a dual rotor motor provided with a permanent magnet rotor serving as an inner rotor positioned most internally in the radial direction, and a rotor with a birdcage coil serving as an outer rotor positioned between the inner rotor and a stator positioned most externally in the radial direction.
The motor disclosed in Patent Literature 4 is provided with a stator including a stator core having a circular stator yoke, a plurality of inner teeth protruding toward radial interior from the stator yoke, a plurality of outer teeth provided in the same number as the inner teeth and protruding toward radial exterior from the stator yoke, inner slots formed between the inner teeth, and outer slots formed between the outer teeth. The stator also includes star-connected or delta-connected three-phase coils wound around the stator yoke between the inner slot and the outer slot.
Also available as linear actuators used in the field of industrial machinery such as those used in robots and conveyors are apparatuses for converting a rotational motion of a motor into a linear motion, and outputting the power in a linear motion direction. For example, the linear actuator disclosed in Patent Literature 5 is provided with a rotational-to-linear motion conversion mechanism including a nut having a threaded inner circumferential surface, a screw shaft having a threaded outer circumferential surface and onto which the nut is screwed, and a movement conversion mechanism for moving the shaft in axial direction upon receiving a rotational force from the nut, while restraining the rotation of the shaft. This actuator moves the screw shaft axially by rotating the nut in the rotational-to-linear motion conversion mechanism together with the rotor of the motor.